1. Field of the Invention
The present invention relates to an electro-pneumatic air pressure regulator which regulates output air pressure in accordance with the magnitude of an analogue input signal (the amount of input electricity).
2. Description of the Related Art
A conventional electro-pneumatic air pressure regulator which includes: a primary pressure (valve-inlet pressure) introduction port; a secondary pressure (valve-outlet pressure) output port; a main valve for opening and closing a communicating conduit via which a primary pressure introduction port and a secondary pressure output port are communicatively connected with each other; a floating piston which moves in accordance with the difference in pressure between the secondary pressure output port and the pilot pressure chamber to open and close the main valve and to release air in the secondary pressure output chamber to the atmosphere; a nozzle conduit via which the pilot pressure chamber is communicatively connected to the atmosphere; a flapper which includes a resilient leaf spring facing an open end of the nozzle conduit; and an electromagnetic drive system which varies the position of the flapper relative to the open end of the nozzle conduit in accordance with the magnitude of an analogue input signal (e.g., electricity), is known in the art.
In this conventional electro-pneumatic air pressure regulator, if a flow path area of a communicating passage between the pilot pressure chamber and atmosphere is constant, a movement of the floating piston toward the secondary pressure output port by a variation in the secondary pressure causes the main valve to open the communicating passage, via which the primary pressure introduction port and the secondary pressure output port are communicatively connected with each other, so that the air in the primary pressure introduction port flows into the secondary pressure output port to thereby increase the pressure in the secondary pressure output port. On the other hand, a movement of the floating piston toward the pilot pressure chamber causes the air in the secondary pressure output port to flow out to the atmosphere to thereby decrease the pressure in the secondary pressure output port. These operations of the electro-pneumatic air pressure regulator maintain the pressure in the secondary pressure output port substantially constant.
On the other hand, if the amount of electricity supplied to the electromagnetic drive system is changed, the leaf spring of the flapper is resiliently deformed in accordance with the amount of electricity supplied to the electromagnetic drive system. This deformation of the leaf spring causes the distance between the flapper and the open end of the nozzle conduit to vary, thus causing a flow path area of a communicating passage between the pilot pressure chamber and atmosphere to vary. As a result, the amount of the air flow from the pilot pressure chamber to the atmosphere varies to thereby vary the pressure in the pilot pressure chamber. Accordingly, the pressure chamber in the secondary pressure output port can be adjusted by changing the amount of electricity supplied to the electromagnetic drive system.
In this conventional electro-pneumatic air pressure regulator, a further improvement in resolving power (the ratio of the variation in the amount of control current (amount of electricity) to the variation of the secondary pressure) is required.